Various types of polymer microparticles have been developed and put in use in a wide variety of fields. The smaller polymer microparticles, the easier the particles aggregate. Accordingly, in view of handling and the like, polymer microparticles of a micron size or more have been frequently used. However, with the recent progress in nano-technology, it has been required to further reduce the size of polymer microparticles. For example, since submicron-size corresponds to the wavelength of visible light, new uses of microparticles have been developed using optical characteristics such as scattering and interference. Of them, for forming a colloidal crystal, in which microparticles are three-dimensionally and densely packed, a narrow particle size distribution, i.e. monodispersibility is also required.
A core-shell microparticle formed of not less than two types of polymers in combination is a functional composite microparticle having a high performance and high functional surface. In the core-shell microparticle, the polymer chains forming the shell with a sufficient density are each connected to the surface of the core microparticle at an end. In a method for producing a core-shell microparticle, recently, attention has been drawn to dense formation of a graft chain using living radical polymerization starting from the surface of a polymer microparticle. The dense formation of a graft chain contributes to sterical repulsion, which suppresses aggregation of the particles.
A method for producing a core-shell microparticle is, for example, proposed in Non-Patent Document 1. In this production method, a microparticle having a functional group such as chloride is formed in advance and then, reacted with a nitroxide compound. In this manner, an alkoxyamine group, which serves as a living radical polymerization initiating group, is introduced into the surface of the polymer microparticle. Subsequently, graft polymerization is performed based on an alkoxyamine group to form a core-shell microparticle.
Furthermore, a method for producing a core-shell microparticle by polymerizing a monomer containing an atom transfer radical polymerization (ATRP) initiating group and divinylbenzene in accordance with precipitation polymerization in an acetonitrile solvent to form a microparticle containing an ATRP initiating group, and performing graft polymerization based on the ATRP initiating group, is disclosed (see, for example, Patent Document 1).
Non-Patent Document 1: J. Polym. Sci. Part A: Polym. Chem., 43, 2145-2154 (2005)
Patent Document 1: Japanese Patent Laid-Open No. 2004-18556 (pages 2, 4 and 5)